The present invention relates to a position measuring device for measuring the relative position of two objects.
Position measuring devices may be employed in machining equipment which measures the relative position of a tool in relation to a workpiece which is to be machined as well as in coordinate measuring machines which determine the position and/or dimensions of a test object.
Such position measuring devices general require a scanning unit which can be slid along an auxiliary guide which is independent from the guide of the object to be measured. The devices also require that the scanning unit be coupled to the object to be measured and/or to a carrier attached to it.
A longitudinal measuring device for measuring the relative position of two objects is known from DE-PS No. 28 10 341 in which the graduation of a graduation carrier is scanned by a scanning unit. The graduation carrier is connected to one object, while another object is connected by means of a carrier. The scanning unit is guided by rigidly mounted guide shoes and rollers on guide surfaces of the graduation carrier and guide surfaces of the housing for the graduation carrier. The scanning unit is forcibly engaged with these guide surfaces by springs which are supported on the housing and on the carrier. The scanning unit is further connected to the carrier via a coupling link having two rotational degrees of freedom around two axes of rotation which are orthogonal to each other and perpendicular to the direction of measurement. The coupling link is in the form of a spring wire mounted parallel to the direction of measurement. This coupling link, however, is only rigid at one end in the direction of measurement, and measurement errors will occur.
DE-PS No. 32 01 887 describes a longitudinal measuring device in which the graduation of a graduation carrier connected to the first object to be measured is scanned by a scanning unit which is connected to the second object to be measured by a carrier. The scanning unit is guided by rigidly mounted guide shoes and rollers on a guide surface of the graduation carrier and on a guide surface of the housing for the graduation carrier. The scanning unit is further connected to the carrier via a coupling, which has a first leaf spring joint having a first rotational degree of freedom around a first rotational axis perpendicular to the direction of measurement, and a second leaf spring joint having a second rotational degree of freedom around a rotational axis orthogonal to the first rotational axis and perpendicular to the direction of measurement, and a linear guide having two translational degrees of freedom perpendicular to the direction of measurement. Both of the leaf springs which run in the direction of measurement similarly are only rigid, at one end, resulting in measurement error. Furthermore, the linear guide is also subject to wear and tear.
It is therefore an object of the present invention to eliminate measurement errors in position measurement devices of the type mentioned above. Other objects of the present invention will become apparent from the following description.